Metabolic products of microorganisms. 184. On the mode of action of cladosporin.

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Abstract
Cladosporin, a fungal [Cladosporium] isocoumarin derivative, strongly inhibits the uptake and incorporation of uracil and leucine into cells of Bacillus brevis and the incorporation of uridine but not leucine into cells of the ascitic form of Ehrlich carcinoma (ECA) of mice. Normal uptake was not restored by removal of the antibiotic. In cells of Escherichia coli A 19-15 (met-) the inhibition of methionine uptake is associated with the cessation of growth. In a methionine-prototrophic revertant from this organism, the uptake of methionine is still inhibited; growth is hardly affected by cladosporin. In vitro no effect on the DNA-dependent RNA polymerase from E. coli and on the RNA polymerase II from wheat germ could be detected. The poly(U)-directed poly(Phe) synthesis was not inhibited by cladosporin. Cladosporin inhibits uptake processes which, for the case of essential nutrients, leads to loss of viability.